1. Field of the Invention
The invention relates to injection molding, and particularly to a process and apparatus for molding an article constructed of multiple materials.
2. Background of the Invention
Various processes for molding articles having multiple materials have been developed. One process that is used for multiple material molding is over-molding. During an over-molding process, a first portion of the final article is molded independently and stored. The first portion is later inserted into a second mold and a second material is introduced. The second material captures and bonds to the first portion to form an article having multiple materials integrated together. The process can be repeated as required for additional materials.
Another process for molding articles constructed from multiple materials is rotational, or shuttle, molding. In a rotational molding process, a first portion of the final article is molded independently. After the first portion is molded, the mold opens and a portion of the mold, typically the core side, with the molded first portion of the article still in place is introduced into a second cavity side of the mold. A second material is then injected into the second cavity and the second material captures and bonds to the molded first portion. This process can also be repeated as required for additional materials.
Transfer molding is another technique that has been used to create molded articles having multiple materials. Similar to the processes described above, a first portion of the article is molded independently. The mold opens and the molded portion is removed from the mold and immediately placed into a second mold, or a second portion of the same mold. The mold closes and a second material is introduced into the second mold or mold portion. The second material captures and bonds to the molded first portion. Again, this process can be repeated as required for additional materials.
Additionally, shifting cavity molding has been used to create molded articles having multiple materials. During a shifting cavity molding process, a first portion of the article is molded. The mold remains closed and a portion of the mold, typically a part of the cavity side, shifts out of its original position. The shifting of the portion of the mold allows clearance for the introduction of a new cavity shape into the space the shifted portion has vacated. The molded portion of the article remains in place in the core side of the mold. A second material is introduced into the new cavity shape which captures and bonds to the first portion molded. This process can be repeated as required for additional materials.
Utilizing multiple molds or multiple cavity sides of a mold creates many disadvantages for multiple material molding. First, the mold design complexity and cost is significantly increased which adds to the total cost of making the articles. Second, the labor required to manufacture the final articles is significantly increased. Additionally, the cost and complexity of the injection molding machines used to perform the processes are increased. Finally, such a process adds to the amount of maintenance required to continually produce acceptable molded articles.
It is, therefore, desirable to provide a simplified and less expensive method and apparatus for multiple material injection molding.